Tammy from Aurora writes, “What’s driving you crazy? Why do more than a dozen empty Aurora Public Schools’ buses drive up and down I-70, east from Colfax to exit #299 Manila Road every morning between 8-9am? They get on at Colfax/Aurora, go about 12 miles east to Manila Road, turn around and head west back to Colfax. This has been the practice for years and I can’t imagine how much unnecessary fuel, hours paid and mileage have been used.”

There is an interesting and simple explanation to what you are seeing. The reason Aurora Public Schools say they drive their buses up and down I-70 is to better maintain the bus fleet and keep their buses running efficiently. That might sound odd when you think of the extra miles and extra fuel as well as the additional wear and tear on the tires as well as other parts of the bus.

“What the viewer is referencing is something we call the "Re-Gen" run on I-70,” says Corey Christiansen, Public Information Officer for Aurora Public Schools. “We started this process several years ago and it has had a tremendous impact on keeping our buses in service.”

In 2015, Aurora Public Schools started the process to replace their existing bus fleet with new diesel buses. The “Re-Gen” run on I-70 started at that time because that was the first time APS had buses equipped with a diesel particulate filter . This filter traps the black plumes of smoke you used to see being emitted from the tailpipe of diesel vehicles. The filters are required to be cleaned through a regeneration process. That process is very similar to you using your self-cleaning oven to burn off anything left in there. To remove the diesel particulate matter, the filter must be heated to over 650 degrees Fahrenheit. If it doesn’t, the filter may clog and have trouble trapping the particulate matter and then the diesel engine breaks down.

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The majority of the Aurora Public School buses stay mainly in the city and do not usually travel more than 35 mph. Plus, the typical school bus spends a considerable time with the engines idling, makes frequent stops and starts, drives with a lack of consistent engine and vehicle speed with a relative light engine load. All of which can impact the efficiency of the DPF. This driving behavior prevents that diesel particulate filter from going through the required regeneration process so it needs the I-70 run to stay clean.

Mechanics tell me replacing the DPF would be much more expensive than cleaning one with the highway run. “The workshop could initiate a “forced regen” and the engine idle speed will increase and the system will execute a stationary regeneration cycle,” says Gerald Dong, Director of AAA Colorado automotive repair programs. “The downside of this is that it might use more fuel and produce more emissions than driving the bus, and it can fill the workshop/yard with smoke and busses sitting and idling at 3,500 RPM for a long time.”

Other school districts make these Re-Gen runs as well to keep their diesel buses in good working order. Bus drivers I’ve talked to from other districts say they have drivers making a similar run to keep the diesel filters clean.

“The Re-Gen run has been very successful at keeping our buses running as efficiently as possible. In fact, since we started using the buses with the DPFs and began the Re-Gen run, our fuel costs have dropped by almost 60%,” Christiansen says. “It ensures that we can provide safe, efficient and effective transportation-related services with on-time delivery for our students to succeed in the classroom.”

"Regen runs to keep your diesel healthy". I'll accept that. Of course it wouldn't need to "regen" if it didn't have all that primitive and marginally effective equipment tacked on to the exhaust. As 01 posted, these devices will "regen" with the vehicle parked--so why the wasted miles and extra expense?
Jack

The bus yard I visited had a furnace to bake the filters. Makes way more sense. Still, owning a diesel with a filter would suck.

My bus had one on it and was equipped with a 208 volt cord to plug it in and burn it off. It is no longer equipped with one. Since it is a 1991 model and registered as an RV, it is EXEMPT. Cue evil laughter now. It also is a very clean burning diesel too.

"Regen runs to keep your diesel healthy". I'll accept that. Of course it wouldn't need to "regen" if it didn't have all that primitive and marginally effective equipment tacked on to the exhaust. As 01 posted, these devices will "regen" with the vehicle parked--so why the wasted miles and extra expense?
Jack

I will say one thing that it’s healthy for the turbo to go out and get on it.

just running them up to warm up actually reduces the amount of ReGen cycles and frequency of ReGen cycles that they wiull go through... ReGen can actually be dangerous to the engine when it is done artificially.. ie where a fuel injector dumps fuel into the last cylinder or right beyind and ignites it to burn off the particulates..

Columbus city schools doesnt do reGen runs.. as a result the local rush truck center is full of nearly new IC CE busses at any given time.. winter time routes sometimes hyave drivers finding their temp gauges stay at 1/4 or below.. the busses never warm up... the drivers rarely properly warm them up during pre-trip.. some have block heaters and are plugged in so the engine temp already has a head start in winter..

this district above running reGen cycles is very creative and a great way to make sure they do warm the busses up... the amount of fuel they burn is minuscule in cost to what it takes to replace a clogged DPF that has gone beyond being able to be 'fired' in a kiln.. even if it is able to be fired clean, the down time for the bus and labor cost to RnR a modern DPF and sometimes the sensors on it freeze to the pipe and have to be destroyed to take the system apart, adding even more cost..

love these guys' simple approach to a widespread problem in the short-trip diesel world.

the pickup truck guys arent immune to this either.. while many diesel trucks are bought to be hot-shots, car-carriers, farm trucks etc, MOST are bought just for the "cool factor" in owning a "big man diesel truck".. and are driven back N forth to work or the grocery store every day, never really warming up.. so they spend a lot of time in artificial ReGen vs just running hot and clean.... guys also like to interrupt the reGen cycles as "they take too long" which will eventually result in a forced ReGen. that if unable to complete will shut the truck down and usually require firing or replacement of the DPF..

“The downside of this is that it might use more fuel and produce more emissions than driving the bus, and it can fill the workshop/yard with smoke and busses sitting and idling at 3,500 RPM for a long time.”

That's not entirely correct. The reason a district will do this is because it's cheaper to pay a driver another hour to do the regen trip per week/bi-weekly then it is to pay a mechanic to do a force regen.

I've never seen a kiln used to "bake" a catalyst, but have seen plenty of places with wash systems to clean the ash out.

Quote:

Originally Posted by cadillackid

just running them up to warm up actually reduces the amount of ReGen cycles and frequency of ReGen cycles that they wiull go through... ReGen can actually be dangerous to the engine when it is done artificially.. ie where a fuel injector dumps fuel into the last cylinder or right beyind and ignites it to burn off the particulates..

Chris, your moving regens still use post-injections to heat up the catalyst to burn off soot. Running down the road would never get the catalyst hot enough to regenerate without them. Granted, you'd likely use fewer post-injections running the bus down the road then you would at idle, but the injections are still needed to get up to temp.

I'd say your moving regens would be better for the vehicle, due to the heat created being blown away by moving through the air, but stationary regens aren't necessarily detrimental.

If the columbus school board was intelligent, they'd pay the drivers to do a lap on 270 every other week. Then again, most districts don't pay the drivers enough as is, and then they sit and wonder why they have such crummy drivers.

For everyone who just had all this stuff go over their head, soot is the black smoke you see coming out the tail pipe when you stomp on the accelerator. The EPA mandates that vehicles need to capture that smoke in a filter. Once the filter is full of soot, they do a "regen" which is where they heat the filter insides up to over 1000*F which burns the soot down into ash. Once the filter is full of ash, the filter is then removed and either washed out, or replaced.

There are several ways to prolong exhaust filter life. The first suggestion is to use less throttle when accelerating. This will reduce the amount of soot that the engine produces. Second, is to always try and let the engine get to operating temperature before running it hard. Third, is to take the vehicle out on a long highway trip every so often so soot accumulation is better managed.

I knew that forced regen still happens sometimes.. but seems the better you warm them up the less often it happens.. never thougth about the fact with the engine operating faster that the hottest gasses are blwon away.. makes perfect sense..

plus there were the non conventional things like international trying to EGR the heck out of everything at first. which caused more issues than it helped..

thing i notice about columbus is routers rarely rotate ever.. down my streets are the same busses morning and afternoon.. and I know the barn they bring em out of on this side of town is not near far enough to warm them up... granted as of the last couple years this area has been running older pre-emissions busses.. (maybe for good reason).. this year an FS-65. circa 02 or so.. and a thomas 3800 with a DT-466E are the ones ive seen so far.. previously they seemed to run Maxxforce 7s down here the most...

some routes require freeway usage.. but i guess for simplicity sake, drivers dont rotate busses during the year? probably safer for a driver to get used to a bus and not have to switch it out every couple weeks..
-Christopher